fix(ci): remove actions/cache steps that require Node.js

The rust:1.89-bookworm container does not include Node.js, causing
actions/cache@v4 to fail with "exec: node: not found". Removed all
cache action steps. sccache still provides intra-job deduplication
when compiling both --features server and --features web.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -11,10 +11,10 @@ on:
 env:
   CARGO_TERM_COLOR: always
   RUSTFLAGS: "-D warnings"
-  # sccache configuration
+  # sccache caches compilation artifacts within a job so that compiling
+  # both --features server and --features web shares common crate work.
   RUSTC_WRAPPER: /usr/local/bin/sccache
   SCCACHE_DIR: /tmp/sccache
-  SCCACHE_CACHE_SIZE: 2G
 
 # Cancel in-progress runs for the same branch/PR
 concurrency:
@@ -60,15 +60,9 @@ jobs:
           curl -fsSL https://github.com/mozilla/sccache/releases/download/v0.9.1/sccache-v0.9.1-x86_64-unknown-linux-musl.tar.gz \
             | tar xz --strip-components=1 -C /usr/local/bin/ sccache-v0.9.1-x86_64-unknown-linux-musl/sccache
           chmod +x /usr/local/bin/sccache
-      - name: Restore sccache cache
-        uses: https://github.com/actions/cache@v4
-        with:
-          path: /tmp/sccache
-          key: sccache-clippy-${{ hashFiles('Cargo.lock') }}
-          restore-keys: |
-            sccache-clippy-
       - run: rustup component add clippy
-      # Lint both feature sets independently
+      # Lint both feature sets independently.
+      # sccache deduplicates shared crates between the two compilations.
       - name: Clippy (server)
         run: cargo clippy --features server --no-default-features -- -D warnings
       - name: Clippy (web)
@@ -118,14 +112,6 @@ jobs:
           curl -fsSL https://github.com/mozilla/sccache/releases/download/v0.9.1/sccache-v0.9.1-x86_64-unknown-linux-musl.tar.gz \
             | tar xz --strip-components=1 -C /usr/local/bin/ sccache-v0.9.1-x86_64-unknown-linux-musl/sccache
           chmod +x /usr/local/bin/sccache
-      - name: Restore sccache cache
-        uses: https://github.com/actions/cache@v4
-        with:
-          path: /tmp/sccache
-          key: sccache-test-${{ hashFiles('Cargo.lock') }}
-          restore-keys: |
-            sccache-test-
-            sccache-clippy-
       - name: Run tests (server)
         run: cargo test --features server --no-default-features
       - name: Run tests (web)